A variety of systems have heretofore been proposed for applying threaded closures to containers. One such system for applying plastic caps to bottles is disclosed in U.S. Pat. No. 5,012,630. Such systems are designed and intended to tighten the closures or caps to a prespecified torque. It is important to maintain the tightening torque within specified limits since an over-tightened cap may rupture the cap or container, while an under-tightened cap may result in leakage of fluid or carbonation.
In general, two techniques have been employed for measuring threaded closure application torque. In the first technique, containers are removed from the conveyor system after the closures or caps have been applied thereto, and transported to a separate station at which the closures are removed while the torque of removal is monitored. Separate and fairly complex measurement apparatus is therefore required, and the torque measurement information is not immediately available to the system operator for implementation of any necessary adjustment. In the other technique, torque measurement apparatus is included in the closure application system itself, measuring application torque as each closure is threaded onto a container. Although the measurement information is immediately available to a system operator, this technique also requires fairly expensive torque measurement apparatus, particularly in application systems having multiple heads.
It is a general object of the present invention to provide a method and apparatus for measuring threaded closure application torque that may be employed for in-line measurement of torque applied by the application system during operation, that measure application torque at system operating speed, that rapidly provide measurement information to a system operator for implementation of any required adjustment, and that may economically be implemented in existing or new closure application systems without redesign or refurbishment of the system itself.